As the machine tool as described above, for example, a machine tool 100 as shown in FIGS. 7 and 8 has been known. The machine tool 100 has a bed 11, a slide 12 disposed on the top of the bed 11 and provided to be movable in an X-axis direction being a horizontal direction (the lower side of the figure sheet is indicated by X1 and the upper side of the figure sheet is indicated by X2), a support member 13 fixedly provided on an X1-side portion of the top of the slide 12, a spindle head 14 supported on the front face of the support member 13 and provided to be movable in a Z-axis direction being the vertical direction, a spindle 15 which is supported by the spindle head 14 to be rotatable its axis with its axis parallel to the Z axis and to a lower end portion of which a tool T is mounted, and a table 16 which is disposed on the top of the bed 11 and provided to be movable in a Y-axis direction perpendicular to both of the X and Z axes and on the top of which a workpiece W is placed.
Further, the machine tool 100 has, in addition to an X-axis guide mechanism 20 for guiding the movement of the slide 12 in the X-axis direction, although not shown in the figures, a Z-axis guide mechanism for guiding the movement of the spindle head 14 in the Z-axis direction, a Y-axis guide mechanism for guiding the movement of the table 16 in the Y-axis direction, an X-axis feed mechanism for moving the slide 12 in the X-axis direction, a Z-axis feed mechanism for moving the spindle head 14 in the Z-axis direction, a Y-axis feed mechanism for moving the table 16 in the Y-axis direction and the a rotation drive mechanism for rotating the spindle 15 about its axis.
The X-axis guide mechanism 20 is configured with two bed-side sliding guide portions 21, 22 (first bed-side sliding guide portion 21 and second bed-side sliding guide portion 22) formed along the X-axis direction on the upper face of the bed 11 with a distance in the Y-axis direction therebetween and two slide-side sliding guide portions 23, 24 (first slide-side sliding guide portion 23 and second slide-side sliding guide portion 24) formed along the X-axis direction on the lower face of the slide 12 with a distance in the Y-axis direction therebetween, and guides the movement of the slide 12 by means of an engagement relationship between the sliding guide portions 21, 22, 23, 24. The slide-side sliding guide portions 23, 24 are formed to hold the bed-side sliding guide portions 21, 22, respectively.
By the way, in the machine tool 100 thus configured, the position of the center of gravity G of a moving structure which is configured with the slide 12, the support member 13, the spindle head 14, the spindle 15 and the tool T is located at such a position as shown in the figures and an offset load acts on the sliding guide portions 21, 22, 23, 24, that is, a larger load acts on an X1-side portion of the second slide-side sliding guide portion 24 than on other portions and the loads acting on the sliding guide portions 21, 22, 23, 24 are not uniform.
For this reason, there are caused a problem that sliding resistance which acts between the X1-side portion of the second slide-side sliding guide portion 24 and the second bed-side sliding guide portion 22 when moving the moving structure (slide 12) in the X-axis direction is so large that the moving structure cannot be moved smoothly, and a problem that uneven wear occurs on the X1-side portion of the second slide-side sliding guide portion 24 and the second bed-side sliding guide portion 22. In addition, there is also a problem that, when a region where sliding resistance is large due to the offset load is distant from the point of force application (drive point) where force is applied to the moving structure by the X-axis feed mechanism, a force causing the moving structure to rotate about the region where sliding resistance is large is generated and accuracy of positioning of the moving structure is thereby reduced.
Therefore, conventionally, a guide mechanism disclosed in the Japanese Patent No. 4190738 has been suggested, for example. This guide mechanism is for guiding the movement of a column which is disposed on a bed to be movable in the forward and backward direction being a horizontal direction and which has its center of gravity on its front side, and it has a bed-side sliding guideway formed along the moving direction of the column (the forward and backward direction) on the upper surface of the bed, a column-side sliding guideway formed along the moving direction of the column on the lower surface of the column and engaged with the bed-side sliding guideway, holing portions for holding lubricating oil formed in the column-side sliding guideway at the column-front-face side and at the column-rear-face side and a lubricating oil supply portion for supplying lubricating oil to the holding portions.
Two said bed-side sliding guideways and two said column-side sliding guideways are formed and both the bed-side sliding guideways and the column-side sliding guideways are spaced in a horizontal direction perpendicular to the moving direction of the column. Each of the holding portions is configured with a land portion and an oil groove, and the holding portion formed at the column-front-face side is formed to have a larger area than the holding portion formed at the column-rear-face side. Further, the lubricating oil supply portion supplies lubricating oil to the holding portion formed at the column-front-face side at a greater flow rate than to the holding portion formed at the column-rear-face side.
In the guide mechanism thus configured, since the holding portion at the column-front-face side is formed to have a larger area than that of the holding portion at the column-rear-face side and lubricating oil is supplied to the holding portion at the column-front-face side at a greater flow rate than to the holding portion at the column-rear-face side, a force supporting the column by means of an oil film of the lubricating oil is greater at the column-front-face side than at the column-rear-face side. Thereby an offset load is prevented from acting on the sliding guideways even when the column having its center of gravity on its front side is moved.